Infrared Excursion...

I'm heading out to the Messum Crater (S21˚25' E014˚ 12') in the next few days, and I'm planning to take my Fotoman PS45, which is fitted with a Rodenstock Grandagon-N 90mm f/6.8. Yipee for me.

I have an appointment with a Welwitschia Mirabilis the age of which I estimate to be around 2500 years. (Ignore the claim in the article that the biggest Welwitschia is only 1.4 metres high; this is nonsense; I know of a few much larger ones...)

I'm planning to take a few infrared photographs with that camera.

While I've shot quite a bit of IR with my Rolleiflex, I've never shot 4x5 sheet film, which in this case is Rollei IR400. So I have a few questions.

2. IR focus correction: There aren't any IR focal correction marks on the lens or the helicoid. Any pointers? I'm anticipating shooting stopped well down (f/32 or so); should I just let depth of field handle it?

3. I have Fidelity film holders. The darkslides are plastic. Should I be worried about IR leakage? I loaded them in a dark bad (duh), in very subdued lighting in a bathroom with no exterior windows (aka my darkroom), immediately transferring the holders to a leather satchel that I normally use to transport my holders to the site. I'm planning to leave the holders in said bag until the last minute, after putting the IR filter on the lens. Should I take any more precautions, or am I already sufficiently paranoid?

General suggestions on shooting IR in the desert? I'm not expecting the 'shiny trees' effect (um, no trees, duh...), but I'd love to hear any other suggestions.